The CT imaging system is widely used in medical imaging and target detection, for example, in security inspection. Compared with the perspective imaging system, the CT imaging system can provide not only a tomogram but also a 3D image of the inspected object, thereby improving detection accuracy. Now the CT imaging system has become mainstream security inspection means in critical places like airport and station. The CT imaging system using a single column or a few columns of detectors has advantages of low cost and small volume. However, Such CT imaging system performs a single-level large-pitch scanning, leading to large interlayer gap and poor definition in the reconstructed 3D image. This makes it difficult for an inspector to find a target in the reconstructed 3D image.
The Ray Casting method is one of the existing volume rendering techniques (Max N. Optical models for direct volume rendering. IEEE Transactions on Visualization and Computer Graphics, 1995, 1(2): 99-108) that are mostly used. The final result of the Ray Casting method is 2D image, and does not record a relation of relative positions of different objects in the image.
The Two-Level Volume Rendering technique (M. Hadwiger, C. Berger, and H. Hauser. High-quality two-level volume rendering of segmented data sets on consumer graphics hardware. In Proceedings of IEEE Visualization 2003, pp. 301-308. Los Alamitos, Calif.: IEEE Press, 2003) or (Helwig Hauser, Lukas Mroz, Gian-Italo Bischi, and Eduard Groller. Two-level volume rendering—fusing MIP and DVR. In proceedings of IEEE Visualization, pp. 211-218. Los Alamitos, Calif.: IEEE Press, 2000.) originates from a synthetic display of segmented and original data in medical image, and requires volume rendering to be in a form of Texture Mapping. the Texture Mapping is worse in imaging quality than the Ray Casting which uses Trilinear Interpolation, and will produce a noticeable transition phenomenon upon viewangle change.
For 3D image rendering in the security inspection field, a method is desirable that can provide display effect in which the target has a higher visual priority. It is further desirable that the spatial position relation of the target in the original data can be reserved to facilitate the inspector in distinguishing the target.